1. Field of the Invention
The present invention relates to a wireless power transmission device and a coil thereof and, more particularly, to a wireless power transmission device capable of detecting metallic foreign object and multiple foreign object detection (FOD) coils thereof for detecting metallic foreign object.
2. Description of the Related Art
A conventional wireless power transmission device basically includes an AC (Alternating Current) to DC (Direct Current) converter, a DC to AC converter and a transmission antenna. An input terminal of the AC to DC converter is used to receive an AC power from mains power. The AC to DC converter converts the AC power into a DC power. The DC to AC converter receives the DC power and converts the DC power into an AC output power. In collaboration with the transmission antenna, the DC to AC converter transmits the AC output power out in the form of electromagnetic waves. Thus, a receiving device with wireless charging functions receives the electromagnetic waves transmitted from the transmission antenna, and converts the electromagnetic waves into a charging power to charge the receiving device in completion of a wireless charging process.
When metallic foreign object enters a range of the electromagnetic waves generated by the wireless power transmission device, the metallic foreign object generates high heat under the effect of electromagnetic field to result in a hazardous situation. Hence, current wireless power transmission devices are capable of detecting metallic foreign object, and the detection techniques of metallic foreign object are adopted to directly measure parameters of electromagnetic waves generated by the transmission antenna, such as power dissipation, efficiency, S-parameters, quality factor and the like. Whether any metallic foreign object enters the range of the electromagnetic waves generated by the current wireless power transmission devices is determined by variation of the parameters of electromagnetic waves.
However, measurement of those parameters is susceptible to a transmission distance of electromagnetic waves. Especially when the size of the metallic foreign object is smaller than that of the transmission antenna, it is difficult to determine if there is ally metallic foreign object entering the range of the electromagnetic waves generated by the current wireless power transmission devices.